1. Field of the Invention
The present invention relates to defect detection in semiconductor alloys. More specifically, the invention is a method of generating X-ray diffraction data for use in the detection of twin defects in “super-hetero-epitaxial” materials (materials in which one material having a first crystal structure is epitaxially grown on a different material having a different crystal structure).
2. Description of the Related Art
Cubic semiconductor alloys including group IV elements (i.e., alloy made with carbon (C), silicon (Si), germanium (Ge), and tin (Sn)) in diamond structure; group III-V elements such as GaAs, AlAs, InAs, GaP, AlP, and InP in cubic zincblende structure; and group II-VI elements such as ZnSe, CdS, and HgTe in cubic zincblende structure are important semiconductor materials used in a wide range of devices, such as Field Effect Transistors (FETs), High Electron Mobility Transistors (HEMTS), Hetero Bi-polar Transistors (HBTs), ThermoElectric (TE) devices, photovoltaic solar cells, and photon detectors.
Typically, such alloys, for example, Silicon Germanium (SiGe), are grown on common silicon wafer substrates. However, the growth of thick (i.e., greater than tens of nanometers), high-quality (i.e., defect free) SiGe layers on a silicon substrate is difficult to achieve because SiGe has a larger lattice constant than silicon. This means that the SiGe layers close to the silicon substrate are strained, and severe defects (e.g., threading dislocations, twin defects such as bulk twin domain and micro-twin defects, cracks, delaminations, etc.) develop in the layers of SiGe that exceed a critical thickness of hundreds of nanometers, because of the lattice mismatch. Thus, at best, only strained SiGe layers with very thin thicknesses (i.e., less than hundreds of nanometers) are utilized for high-quality electronic device fabrication. Similar results are observed for other material combinations.
In our commonly filed patent applications referenced above, which have been incorporated into this disclosure by reference, we describe a number of methods for making a broad range of super-hetero-epitaxial materials. For example, such materials may include new group IV, group III-V, group II-VI and other semiconductor alloys aligned in the [111] direction, on substrates with crystal structures having trigonal or hexagonal space group symmetry, As will be explained later in this disclosure, other useful super-hetero-epitaxial combinations are possible as well.
While such methods can yield high-quality, either strained or lattice-matched semiconductor alloys based on a wide variety of selected materials and substrates, problems can develop during fabrication that can affect the quality of the fabricated material. For example, twin defects can be formed in such materials by one or both of (i) double position defects due to crystal structure differences between the epilayer and substrate, and (ii) stacking faults during epilayer growth. Therefore, to examine and/or assure the quality of the resulting rhombohedrally aligned material, it is necessary to check the alloy for both bulk twin domain and micro-twin defects.
Currently, twin defect detection is accomplished by a “transmission electron microscopy” (TEM) analysis. However, TEM results in destruction of the material and is, therefore, only suitable for microscopic laboratory analysis or as a periodic or random sampling check on semiconductor materials being mass-produced. This method is therefore not suitable for generating data for quality control during the fabrication of semiconductor wafers.
Accordingly, for purposes of development of materials and devices to take advantage of the technologies disclosed in our commonly-filed disclosures listed above regarding rhombohedral growth of both strained and lattice-matched cubic semiconductor alloys of a range of group IV, group III-V, group II-VI and other materials on the c-plane of trigonal substrates, as well as numerous materials based on other super-hetero-epitaxial combinations, there is a great need for a nondestructive method for detecting, and generating data regarding, twin defects in such materials.